Location matters. Last month, a new report from the Institute of Medicine confirmed what Dartmouth’s researchers have been telling us for more than three decades: health care spending varies across regions. More recently, as Dartmouth’s investigators have drilled down into othe data,, they have shown that even within a region, Medicare spends far more per beneficiary in some hospitals than in others.

Some health care analysts claim that as a nation, we spend far more on health care than any other developed country because we over-pay for everything—from statins to surgery. (A landmark article that appeared in Health Affairs in 2003 put it this way “It’s the Prices Stupid!” )

Others put more emphasis on overtreatment. Up to one-third of Medicare dollars are squandered, physicians like Dartmouth’s Dr. Elliott Fisher, Boston surgeon Atul Gawade and former Medicare director Dr. Don Berwick argue. As Fisher puts it, “hospital stays in the U.S. may not be as long as in some other countries, but more happens to you while you’re there.” (Note: the authors of “It’s the Price’s Stupid” also point out that care in the U.S. is “more intensive.”)

I agree that both theories are true: We have managed to devise a health care system where we both over-pay AND are over-treated. The Institute of Medicine report that came out at the end of July supports this thesis.

But, he adds, “There is one important difference between Medicare and commercial insurance, the Institute found, and that is in the causes of spending variation. With commercial insurance, spending is higher in some areas because of markups — that is, the difference between the charge for a service and the cost of providing that service.

“Seventy percent of the variation in commercial spending was attributed to differences in markups, which in turn probably reflect local differences in market power among hospitals and other providers relative to insurance companies and beneficiaries.”